Heteropolycatalyst system



United States Patent 09,561 HETEROPOLYCATALYST SYSTEM Natale Ferlazzo,Giorgio 'Caporali, and Nicola Giordano,

Milan, Italy, assignors, by mesne assignments, to Montecatini EdisonS.p.A., Milan, Italy No Drawing. Original application Aug. 13, 1963,Ser. No. 301,880, now Patent No. 3,370,083, dated Feb. 20, 1968. Dividedand this application Apr. 27, 1966, Ser. No. 567,023

Claims priority, application Italy, Aug. 23, 1962, 26,538/ 62 2 Claims.(Cl. 252-439) ABSTRACT OF THE DISCLOSURE A catalyst system consistingessentially of at least one heteropolycompound selected from the groupwhich consists of Bl Th oMomovzoo Te Ce Mo V O and x 100 20 Y where xrepresents a number in the range from 1 to 180 and y represents a numberin the range from 370 to 730.

This application is a division of Ser. No. 301,880, filed Aug. 13, 1963,and now Patent No. 3,370,083.

The present invention relates to a catalyst for preparing nitriles. Moreparticularly, the invention relates to an improved process for theproduction of unsaturated nitriles using catalysts containing anheteropolycompound.

In the technical literature processes have already been described inwhich an olefin is reacted with ammonia and oxygen in the presence ofspecific catalysts, in order to obtain unsaturated nitriles. I

The known catalysts comprise different elements, mainly as combinationsof their oxides or in the form of salts, such as the bismuth, tin andantimony salts of the molybdic, phosphomolybdic and phosphotungsticacids; the molybdenum, cobalt and tellurium oxides; the molybdenum andtellurium oxides; the tungsten and tellurium oxides; the telluriumoxide; the molybdenum and chromium oxides; the molybdenum, arsenic andbismuth oxides; the mixtures of molybdenum, vanadium, chromium,maganese, cobalt, nickel, copper, iron, tellurium, selenium, bismuth,silver, gold and aluminum oxides; phosphoric acids activated bydifferent elements such as those above mentioned; and the mixtures ofbismuth, phosphorus, vanadium, manganese, chromium, iron, cobalt andnickel oxides.

In general, the known processes are not fully satisfactory. Among theirdisadvantages is relatively low selectivity, that is, low yields of thedesired unsaturated nitrile, coupled with the formation of large amonutsof carbon oxides, and undesirable by products such as unsaturatedaldehydes, acids, ketones, saturated nitriles, hydrogen cyanide.

The by-products obviously represent a loss of substance besides makingthe recovery of the desired unsaturated nitrile, in a pure state, morediflicult.

A further disadvantage of conventional processes is, in general, a lowconversion of the olefin input for each pass; hence, the catalyst has alow output with the result that a re-cycling of the olefin is required.

Still another disadvantage of the known processes is represented by theside-reactions of the ammonia, which 3,409,561 Patented Nov. 5, 1968 icelargely take place when using the known catalysts at the workingtemperatures. Moreover in the known processes, in order to obtain goodselectivity, large amounts of ammonia in relation to the olefin arerequired.

Still another disadvantage of the known processes is the relatively longcontact time which is required for obtaining a satisfactory conversionof the starting olefin.

A further disadvantage is the limited life of the catalysts used in theknown processes, which makes frequent regenerations of the deactivatedcatalyst necessary.

Thus, the object of the present invention is to provide an improvedcatalyst for the production of unsaturated aliphatic nitriles with highyields, by reacting an olefin with oxygen and ammonia, without howeverthe attendant disadvantages of the known processes.

Another object of the present invention is to provide a process and acatalyst which allow higher yields of unsaturated nitrile than hithertoobtainable through this type of reaction.

A further object of this invention is to provide a process and acatalyst which allow a higher conversion for each passage withrelatively short contact times and Without reducing the selectivity ofthe reaction.

Still another object of this invention is to provide a process and acatalyst with which to obtain the maximum possible utilization of theammonia fed in, by avoiding its consumption in side-reactions.

Still a further object of this invention is to provide a catalyst soimproved, that it can be used continuously without any loss of activityand that in consequence thereof, it does not require frequentregeneration.

The process according to the present invention offers considerableadvantages in comparison to the known processes. In fact, it has beenfound that, with the new catalytic complexes according to the presentinvention, it is possible to obtain high conversion of the olefinwithout, however, reducing the yield of unsaturated nitrile obtained inthe reaction.

A particularly important advantage lies in the high degree ofselectivity shown by the catalysts according to the present invention.The term selectivity is used to indicate that side-reactions take placeonly to a very small extent and that, therefore, only extremely smallquantities of by-products and carbon oxides are formed.

The absence of side-reactions, which are highly exothermic, makes thethermic control of the process a relatively simple matter, thus avoidingthe necessity of complicated equipment and/or technique for dissipatin'gintense reaction heat.

Still another advantage is found in the short catalytic contact timerequired, which provides a higher productivity by the catalyst.

Still a further advantage lies in the high resistance of the catalyst todeactivation; in consequence whereof the catalysts according to thepresent invention have a long life without any appreciable loss ofactivity.

The present invention resides in a catalized process for obtaining anunsaturated nitrile, by reacting an olefinic hydrocarbon in the gaseousphase with gaseous ammonia and gaseous oxygen, or oxygen-containinggases, on a catalytic complex, which will be described in detail furtheron, at temperatures ranging from 300 C. to 600 C., under substantiallyatmospheric pressure.

The catalytic complexes according to the present invention can beconsidered as resulting from the salification (i.e. salt-forminginteraction) of a particular heteropolycompound with an element chosenfrom the group consisting of bismuth and tellurium.

Asit is known, the heteropolyacids are considered as resulting from twoor more molecules of two or more different acids by elimination of watermolecules (heterodiacids, heterotriacids, heterotetracids); moreparticularly they may be considered as resulted from the union of adefinite number of molecules of acid anhydrides, particularly W M00 andV 0 (whose metals are usually defined as coordinated elements) withmolecules of a second acid that supplies the central atom (usuallydefined as coordinating element) of said polyanionic complex.

The catalytically active heteropolyacids according to the presentinvention, are just those heterotriacids which have as coordinatingelement a rare-earth element of the lanthanide series, such as cerium,and an element of the actinide series such as thorium, and which have ascoordinated elements molybdenum and vanadium. Such heteropolyacidscorrespond to the following formulae:

In order to obtain catalysts according to this invention, theseheterotriacids are salified with one of the elements chosen from thegroup consisting of bismuth and tellurium. The salification is effectedby reacting a compound of the salifying element with the heteropolyacidor with the ammonium salt of said heteropolyacid.

According to this invention, in the salification of the heteropolyacidor of its ammonium salt an excess or a deficiency in the compound of thesalifying element with respect to the theoretical quantity required canalso be used. Surprisingly it was found that also the catalyst preparedwith an excess or a deficiency in the salifying element are quiteeffective for executing the process according to the invention.

Consequently, the catalysts suitable for operating according to theprocess according to the present invention may be convenientlyrepresented by the following formulae:

X IO MO ZO y Me Th Mo V O wherein Me represents an atom of an elementchosen from the group consisting of bismuth and tellurium, x representsa number comprised within the interval from about 1 to about 180, yrepresents a number that assumes particular values comprised between 370and 730, depending on the valency status of the other elements (Ce, Th,Mo, V, Me) and depending on the values of x.

The catalytically active heteropolycompounds may be used by themselvesor mixed with each other.

These heteropolycompounds proved to be both effective as such, as wellas in admixture with a suitable support. Furthermore, it was found thatthey ar effective both in a fixed and in a fluid bed.

The process according to the present invention may be used withaliphatic olefins having straight or branched chains with at least threecarbon atoms, and at least one methylic group in an a-position withrespect to the double bond.

The process is particularly effective and gives excellent yield whenpropylene is used for obtaining acrylonitrile and isobutylene formethacrylonitrile.

The olefin may be used in the pure state; however, it has been foundthat the reaction succeeds equally well when the olefiins are dilutedwith paraffinic hydrocarbons which do not react under the conditions ofthe process and behave as inert diluents.

The oxygen necessary for the reaction may be supplied either in the purestate or in the form of gases containing it, for instance, air. Thislatter embodiment offers some advantages deriving from the nitrogen thataccompanies the oxygen, and which serves usefully as a diluent, as willbe seen further on.

Given the exothermic character of the reaction, it may be useful or evennecessary to dilute the reacting gases with inert gaseous substances.Examples of such substances, whose use was found convenient in theprocess according to this invention, may be parafiinic hydrocarbons (forinstance those that may be found already mixed with the raw olefinused), nitrogen, carbon dioxide, steam etc.

As mentioned above, the use of air instead of oxygen in the process alsoprovides nitrogenwhich acts as an inert diluent. Even the olefin itselfacts as an inert diluent when it is used in excess. j

The operational procedures, the quantity etc. of diluent to be used inthe process of this invention depend obviously on different factors; forinstance: on the reaction conditions, on the amount of the achievedconversion and, consequently, on the quantity of a developed heat, onthe selectivity in the sense that, where'there is a low selectivity, themain reaction is accompanied by side reactions which, being moreexothermic that the main reaction, require great r quantities of diluentfor thermal control of the process; and finally on the techniqueapplied, that is, whether the reaction is carried out on a fixed or on afluid bed, as well as upon the equipment used.

Thanks to the exceptionally high selectivity of the catalysts accordingto the invention, which strongly inhibit the highly exothermicside-reactions, the use of a supplementary diluent in the fed gaseousmixture may be reduced to very low values, or even omitted altogether,especially when air is used, since the nitrogen present in the air ingeneral is sufficient for controlling the exothermicity of theside-reactions.

The quantity of oxygen or of the gases containing it, used in relationto the quantity of employed olefin, may vary within very wide limits. Inthe preferred case the molar ratio between the oxygen and the olefin isbetween 0.5 and about 2.5. The quantity of ammonia to be used withrespect to the olefin may vary within wide limits. However, thepreferred molar ratio between the ammonia and the olefin lies betweenabout 0.3 and about 2.

In order to achieve a maximum of ammonia utilization, the lattersquantity should be sufficient at least for completing the reaction; onthe other hand, a great excess of -ammonia would result in a waste ofit.

It has been noted that certain gaseous mixtures of olefins, oxygen andammonia, characterized by specific ratios of the components may behaveas explosive mixtures. However the process according to this inventionis operative also within the limits represented by said explosivemixtures.

The high selectivity of the catalyst according to this invention allowsthe maximum possible utilization of the ammonia present in the reaction,so that, in order to ensure a complete reaction, only a small excess ofammoma with respect to the reacting olefin will be required.

While the reaction is generally effected with excellent results underatmospheric pressure, it can also be carried out under pressure higherthan atmospheric pressure. Thus, the process may be carried out attemperatures ranging from about 300 C. to about 600 C.; however,temperatures lying between 400 C. and 550 C. are preferred because atsuch temperatures the reaction rate is so high that high conversions areachieved also with relatively short contact times, as it will be seenhereunder and as it will be illustrated by the examples given furtheron.

The contact time (expressed as the time during which a volume unit ofthe gaseous mixture fed in, measured under the average conditions oftemperatures and pressure existing in the reactor, remains in contactwith an apparent volume unit of the catalyst) may vary within widelimits, for instance from 0.05 to 20 seconds, but it has been foundthat, thanks to the high activity of the catalyst, contact times lessthan 1 second are sufficient for obtaining a high conversion, so thatthe time range preferred for the execution of the process according tothis invention lies between about 0.1 and about 3 seconds.

The heteropolycompounds used as catalysts in the process according tothe present invention may be obtained in the following way; first thefree heteropolyacid or its ammonium salt is prepared by following thegeneral methods described by the specialized literature for theirpreparation. This heteropolyacid or its ammonium salt is then reactedwith a compound of the desired salifying element in a liquid reactionmedium and in the presence of small quantities of a strong acid.

The salifying-element-containing compounds are, according to theinvention, oxides, hydroxides or salts of organic and inorganic acids ofbismuth and tellurium preferably soluble in a solvent chosen from theclass consisting of water, alcohols, ethers and esters.

The two reactants, that is the heteropolyacid or the ammoniumheteropolysalt and the salifying-element-containing compound are reactedin a stoichiometric quantity in order to obtain as the reaction productthe heteropolysalt of the desired element; it is, however, also possibleto use an excess or a deficiency with respect to the theoretical valueof the compound of the salifying element. In any case, the catalystsprepared by using an excess or a deficiency of this reactant, arecomprised within the limits defined by the formulae previously quoted.

The reaction may be effected between the solution or the suspensions insuitable solvents of the two reactants, depending on their solubility.The preferred solvent is water, though also other solvents may be used,such as oxygen-containing organic solvents and particularly alcohols,ethers, and esters. The reaction is effected in the presence of strongmineral acids and, in particular, nitric acid.

The conditions at which the reaction is carried out (for instancetemperature, stirring, order of feeding of the reactants etc.) are notcritical for obtaining catalysts usable in the process according to theinvention.

According to another embodiment it is possible to react the compound ofthe salifying element with the ammonium heteropolysalt in the samereaction medium in which said ammonium heteropolysalt has been obtained.Such embodiment is carried out by mixing first the solution of a salt orof an acid containing the coordinated elements with a solution of anacid or a salt containing the coordinating elements, and by adding thento the mixture thus obtained the solution of a compound of the salifyingelement.

Anyhow obtained, the catalyst may be either used alone (i.e. without anysupport), or it may be conveniently supported on a suitable carrier.

In case it is not desired to make use of a support, the product of thecatalyst preparation reaction is evaporated to dryness, for instance byheating the catalyst to 110 C., and then activated by heat.

The activation consists in heating the catalyst at a temperature between400 C. and 600 C. for a period of 5 to 20 hrs. The activationtemperature must be equal to or higher than the temperature at which thecatalyst will be operating in the process for obtaining the nitriles.

To the catalyst may be given a particular shape and/ or size throughgrinding, sieving, pressing into tablets etc. as it is well known to anyexpert of the art. Also the wellknown spray-drying technique can beconveniently applied.

Though the catalysts according to the invention may be used without anysupport, it is preferable to use supports which contribute to theeffectiveness and the life of the catalyst. Suitable supports for thispurpose may be silica, alumina, alundum, fireclays or like materials,both in the form of powders of suiable size or of tablets, pellets,granules, or even as a gel,- such as silica or alumina gel.

Among the supports proved particularly convenient those which possess aso-called open-structure for instance the silica aerogels. Thetechniques most suitable for depositing the catalysts on supports arewell known to those working with catalysts and also go beyond the fieldof this invention. They are, however, easily applicable to the catalystsconforming to the present invention.

Also the catalyst deposited on a support, like the unsupported catalyst,must be activatedby heat according to the procedure above described.

As it is known to any expert of the art, in the course of thepreparation, easily decomposable organic substances such as oils,glycerol, polyvinyl acetate, polyvinyl alcohol, which by decompositionduring the activation phase give to the catalyst a-higher porositydegree can be added.

Hereunder some examples illustrating the inventive concept of theinvention are given.

In the given examples the percentage of the gaseous feeding mixture aregiven by volume, while the percentages in yield are referred to themoles.

The results given in the examples are-inferred both by means ofchromotographic analysis as well as by quantitative, volumetric andgravimetric analysis or by gasvolumetric analysis.

EXAMPLE 1 A catalyst based on the tellurium salt of thecericmolybdo-vanadic acid is prepared in the following way: 30.4 gramsof ammonium paramolybdate are dissolved in 125 ml. of water and thesolution then passed over a strong acid cation-exchange resin bed (forinstance such as those known under the commercial name of Am-berlite IR120. To the solution thus obtained 11 grams of sodium meta-vanadate areadded, and then it is brought to the boiling point. Thereupon a solutionof 9 grams of ammonium ceric nitrate in ml. of water or a solution of 9grams of cerium carbonate in water containing ammonium carbonate isadded dropwise; the whole is then heated for one hour with refluxing andthen filtered. The filtrate is then concentrated and an extraction inthe presence of strong acid with ethylic ether is carried out. Theetheric solution of the heterotriacid thus obtained is then evaporatedto dryness and to the residue is then added enough water for dissolvingit; the solution is then evaporated until crystallization sets in. Theproduct thereby obtained corresponds to the formula:

In order to obtain the tellurium salt of said heterotriacid, 0.1 grammolecular weight of this, dissolved in water, are salified with 0.2 gramatoms of tellurium, that is they are added to 25.5 grams of metallictellurium dissolved in nitric acid; 210 grams of a silica aerogel (knownunder the commercial denominations of Aerosil, Cab-o-Sil, Sant-o-Cel")which acts as a support, are then added. The mass thereby obtained isthen dried by heating it up to C. and finally activated by heating at490 C. for 12 hrs.

After a suitable subdivision of the catalyst so that it may work as afluid bed, the catalyst is put into a reactor and over it a gaseousmixture composed of 8.8% of propylene, 63.1% of air, 6.2% of ammonia and21.9% of steam is allowed to flow.

The contact time of this mixture with the catalyst is 0.6 second, thetemperature is maintained constant at 423. C.

The yield in acrylonitrile is of 80.1% with respect to the convertedpropylene; at the same time acetonitrile and acrolein in the respectiveamounts of 3.3% and 1.8% are formed.

EXAMPLE 2 A catalyst based on tellurium ceric-molybdo-vanadate supportedon a silica aerogel is prepared by pouring on 180 grams of said aerogel(known under the commercial denominations of Aerosil, Cab-o-Sil,Sant-o-Cel) a solution of 176.5 grams of ammonium paramolybdate, asolution of 54.8 grams of ammonium ceric nitrate, a solution of 23.4grams of ammonium metavanadate and a solution obtained by dissolving 1.3grams of metallic tellurium in nitric acid.

The whole is then dried and the catalytic mass thus obtained isactivated by heating same at 510 C. for about 12 hrs.

After reduction to the desired size, the catalyst is used as a fluid bedin a suitable reactor at a temperature of 478 C.

Over this catalyst a gaseous mixture containing 8.5% of propylene, 62.5%of air, 4% of ammonia and 25% of steam is allowed to pass, with acontact time of 0.6 second.

From the analysis of the products it is found that 71% of the propyleneconsumed was transferred into acrylonitrile, 5.4% into acrolein, 1.1%into hydrogen cyanide and 15.7% into carbon oxides.

EXAMPLE 3 A catalyst based on the bismuth salt of ceric-molybdovanadicacid is prepared in the following way: to the aqueous solution of thefree heterotriacid (0.1 mole), prepared as described in Example 1, isadded an aqueous solution of 129 grams of bismuth nitrate acidified with38 cc. of nitric acid and 26.8 grams of a silica aerogel (Aerosil,Cab-o-Sil, Sant-o-Cel).

The mass thus obtained is then spray-dried in the usual equipment;thereby obtaining directly the catalyst in a finely subdivided status,suitable for use as a fluid bed.

After activation by heating at 540 C., for about 12 hrs., the catalystis put into a reactor and brought into contact with a gaseous mixturecontaining 8.2% of propylene, 62.1% of air, 5.7% of ammonia and 24% ofsteam.

The temperature is maintained at 455 C., while the contact time is 0.6second.

It was found that 71.5% of the converted propylene is transformed intoacrylonitrile, 5.9% into acetonitrile and 1.3% into acrolein.

EXAMPLE 4 A catalyst based on ceric-molybdo-vanadate of bismuth isprepared in the following way: to the aqueous solution of 0.1 mole ofthe ceric-molybdo-vanadic heterotriacid, prepared as in Example 1 isadded as aqueous solution of 436 grams of bismuth nitrate acidified withnitric acid and then 390 grams of silica aerogel.

The mass thus obtained is dried, then activated by a prolonged heatingat 550 C., and finally subdivided into a size suitable for its use as afluid bed.

The catalyst thus prepared, is then brought into contact in a reactor,at a constant temperature of 490 C., and for a contact time of 0.8second, with a gaseous mixture consisting of 8.9% of propylene, 7.1% ofammonia, 66.7% of air, 0.5% of propane and 16.8% of steam.

It was found that 66.1% of the propylene introduced is converted, andthat 84.2% of the converted propylene is transformed into acrylonitrile,while only 2.9% of it is transformed into acetonitrile and only tracesof acrolein are formed.

EXAMPLE 5 Two catalysts herein designated catalyst A and catalyst B,both based on the bismuth salt of eerie-molybdovanadic acid, andditferent from each other for the different concentration of thecatalytically active compound with respect to the support, are preparedas follows:

On 33 grams of a silica aerogel for the catalyst A and on 8.5 grams of asilica aerogel for catalyst B, a warm aqueous solution of 35.3 gramsammonia paramolybdate, a solution of 4.7 grams of ammonium vanadate, anaqueous solution of 0.02 gram mole of ammonium ceric nitrate and anaqueous solution of 87.3 grams of bismuth nitrate acidified with nitricacid are poured.

The mixture thus obtained is evaporated to dryness and the mass thusobtained is activated by heating at 540 C. for 12-18 hrs.

The catalyst, suitably subdivided, is used in a reactor operating inaccordance with fluid-bed techniques.

The results obtained are summarized in the following table:

Catalyst Catalyst Volumetric composition of the gaseous mixture fed in,in percent:

Propylene l0. 9 8. 8 Air 80. 4 65. 5 8. 7 7. 1 18. 6 Contact time, insecond 0. 85 0. 8 Reaction temperature, C 502 502 Transformed propylene,with respect to that fed in, percent 74 73 Percent yield with respect tothe transformed propylene:

Acrylonitrile 82. 5 84. 4 Acetonitrile 3. 3 3. 1 Acrolein 0. 9 1Propylene transformed into carbon 0 des with respect to the propylenefed, in percent 8. 5 6. 5

EXAMPLE 6 Over a catalyst prepared like that described in Example 4 andlikewise used in a reactor operating with a fluid bed, is passed agaseous mixture composed of 9.6% propylene, 13.5% oxygen, 6.7% ammoniaand 70.2% of steam.

The contact time of this mixture on the catalyst is 0.7 second; thetemperature is maintained constant at 501 C. 60.6% of the propylene fedin is converted. The yield of the acrylonitrile is with respect to thepropylene fed in, While that of the acetonitrile is 5.1%; only traces ofacrolein are obtained. The carbon oxides formed amount 7.3 of the fedpropylene.

EXAMPLE 7 A catalyst based on bismuth ceric-molybdo-vanadate is preparedas follows: To the aqueous solution of 0.1 mole of ceric-molybdo-vanadicheterotriacid, prepared as in Example 1, is added a solution whichcontains nitric acid and 436 grams of bismuth nitrate.

The mass is evaporated to dryness, then activated by heating at 540 C.and finally subdivided so that it may be used as a catalytic fluid bedin a reactor.

Over this catalytic fluid bed a gaseous mixture consisting of 9.1%propylene, 6.3% ammonia, 66.4% air and 18.2% of steam is made to pass ata constant temperature of 463 C., for a contact time of 0.8 second.

It will be found that 64.4% of the propylene fed in is converted; withrespect to this a yield in acrylonitrile of 78.9% is obtained,accompanied by 4.4% of acetonitrile and 4% of acrolein.

EXAMPLE 8 Over the catalyst B, prepared as described in Example 5, agaseous mixture composed of 5.9% isobutene; 8.1% oxygen, 3.5% amonia and82.5% vapor is made to pass.

The contact time of this mixture with the catalyst is of 0.58 second.The temperature is maintained constant at 425 C.

The yield in methacrylonitrile with respect to the isobutene consumed,is 51%, simultaneously 15.9% of methacrolein is formed.

EXAMPLE 9 A catalyst based on the bismuth salt of thorio-molybdovanadicacid is prepared as follows: Firstly, free thioriomolybdo-vanadicheterotriacid is prepared proceeding in the manner described in Example1 for the preparation of the ceric-molybdo-vanadic acid, of course withthe difference that instead of the cerium nitrate or carbonate, 9 gramsof thorium nitrate in an aqueous solution are used.

To the aqueous solution of 0.1 mole of the free thoriomolybdo-vanadicheterotriacid thus prepared, is added a solution acidified with nitricacid of 129 grams of hismuth nitrate, and on the mixture thus obtained,are

poured 250 grams of a silica aerogel (Aerosil, Sant-o- Cel, Cab-o-Sil).

The mass is evaporated to dryness by heating to 110 C. and then the drycatalytic mass is activated by a prolonged heating at 540 C. for about12 hrs.

The catalyst thus obtained is then crushed and used as a fluid bed.

A gaseous mixture containing propylene, air, ammonia and vapour in therespective amounts of 8.6%, 61.5%, 4.3% and 25.6% is passed over thecatalyst, for a contact time of 0.75 second.

It is found that at the constant temperature of 456 C., 70.2% of theconverted propylene will be acrylonitrile.

EXAMPLE A catalyst based on bismuth thorio-molybdo-vanadate is preparedas follows:

Onto 17.5 grams of a silica areogel (known under the commercial names ofAerosil, Cab-o-Sil, Sant-o- Cel) is poured a lukewarm aqueous solutionof 70.6 grams ammonium paramolybdate, an aqueous solution of 9.4 gramsof ammonium metavanadate, an aqueous solution of 22.1 grams of thoriumnitrate, an aqueous solution of 174.6 grams of bismuth nitrate acidifiedwith nitric acid. The mixture thus obtained is evaporated to dryness byheating to 110 C., the solid catalytic mass is then activated by heatingfor about 12 hrs. at 540 C.

After suitable subdivision, the catalyst is used as a fluid bed in areactor into which is fed a gaseous mixture composed of 6.7% propylene,63.7% air, 5.4% ammonia and 24.2% steam.

The temperature is maintained at 505 C., the contact time of the gaseousmixture on the catalyst is 0.6 second.

It will be found that 54.5% of the fed-in propylene is converted. Theyield in acrylonitrile with respect to the converted propylene is 80.2%,while the yield in acetonitrile is 3%.

8.5% of the propylene fed in is transformed into carbon oxides.

EXAMPLE 11 A catalyst based on the tellurium salt of thethoriomolybdo-vanadic acid is prepared as follows: Firstly freethoriomolybdo-vanadic heterotriacid is prepared by proceeding asdescribed in Example 8.

The free heterotriacid is salified with tellurium by adding to anaqueous solution of 0.1 mole of said heterotriacid a solution obtainedby attacking 25.5 grams of metallic tellurium with nitric acid; as thesupport, 220 grams of a silica aerogel are then added.

The mass thus obtained is then spraydried and then activated by heatingfor 12 hrs. at 500 C.

Over the catalyst thus prepared is passed a gaseous reactant mixture:8.7% propylene, 63.2% air, 6.1% ammonia and 22% steam, regulating itsquantity in such a way as to have a contact time of 0.85 second.

It will be found that at the constant temperature of 452 C. the yield inacrylonitrile with respecfl to the propylene which has reacted is 79.5%;that the acrylonitrile is accompanied by a highly reduced quantity ofacetonitrile, equal to 1.8% of the reacted propylene.

We claim:

1. A catalyst system consisting essentially of at least oneheteropolycompound selected from the group which consists of x io ioo zoTe ce oMo oovzoo and Te ThmMO oovgoo where x represents a number in therange from 1 to 180 and y represents a number in the range from 370 to730.

2. A catalyst system as defined in claim 1, further comprising a supportfor said heteropolycompound selected from the group which consists ofsilica and alumina.

References Cited UNITED STATES PATENTS 12/ 1965 Giordano et a1. 252-4397/ 1966 McDaniel et al 252462

